"I didn't get that. Do You think that this is a benefit over meshes?"
Meshes can have color filters applied at the row/column.
It would be faster than perpixel, but its per vertex instead.
It really wouldn't work here, unless the texture is really small.
It would be useful if say you wanted to add lighting.
As to increasing the quality by basically subdividing it, yes that will add some, but keep in mind there is the hardware limitation, around 64x64.